Nonlinear piezoelectricity in poly(vinylidene fluoride)

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Abstract
The piezoelectric strain constant d32 of uniaxially stretched and poled PVDF [poly(vinylidene fluoride)] was found to be a nonlinear function of the applied stress or strain. The nonlinear behavior manifests itself, in good agreement with the predictions of the phenomenological theory of nonlinear piezoelectricity, by a piezoelectric constant d32 which decreases with increasing stress and by the occurrence of the second harmonic component (2f) of the polarization for a sinusoidal stress (frequency f). The nonlinearity has been tentatively attributed to the stress-induced variation of the distance between parallel chains in the PVDF crystals and their interfaces, causing a reduction of the dipolar and nondipolar interchain interactions.